US6967930B2 - Method and apparatus for transmitting data packets - Google Patents

Method and apparatus for transmitting data packets Download PDF

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US6967930B2
US6967930B2 US09/910,802 US91080201A US6967930B2 US 6967930 B2 US6967930 B2 US 6967930B2 US 91080201 A US91080201 A US 91080201A US 6967930 B2 US6967930 B2 US 6967930B2
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packets
update
context
operable
header
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US20020027882A1 (en
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Carsten Burmeister
Rolf Hakenberg
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Godo Kaisha IP Bridge 1
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Matsushita Electric Industrial Co Ltd
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Assigned to GODO KAISHA IP BRIDGE 1 reassignment GODO KAISHA IP BRIDGE 1 ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: PANASONIC CORPORATION (FORMERLY MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.)
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
    • H04L69/04—Protocols for data compression, e.g. ROHC
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/40—Network security protocols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
    • H04L69/22—Parsing or analysis of headers

Definitions

  • the invention generally relates to a method and apparatus for transmitting data packets over an unreliable channel, and in particular to transmitting data packets having compressed headers.
  • RTP Real-time Transport Protocol
  • UDP User Datagram Protocol
  • IP IP Multimedia Subsystem
  • RTP has been developed for fixed networks, it may nevertheless be used in mobile networks.
  • one problem in using RTP over mobile networks is the limited bandwidth in the mobile channel. This is because each of the protocols RTP, UDP and IP has its own header.
  • a packet will then, in addition to link layer framing, have an IP header of 20 bytes, a UDP header of 8 bytes, and an RTP header of 12 bytes, thus summing up to at least 40 bytes.
  • header compression protocols remove the redundancy of the header and encode the information in an efficient way. This may lead to a compression of the original header down to one byte in the best case.
  • FIG. 1 A system using a header compression protocol is illustrated in FIG. 1 .
  • the transmitter comprises a compressor 100 which is used for compressing the original header.
  • the compressed header is then transmitted to the receiver and is there decompressed by the decompressor 110 .
  • the context 120 is the state which the compressor uses to compress the header.
  • the context is a set of variables and consists basically of an uncompressed version of the header fields of the last header. Besides the actual header fields, the context comprises additional variables, such as first order differences of header fields that have been detected to be constant for a series of successive packets.
  • the context can also contain additional information describing the packet stream, for example the typical inter-packet increase in sequence numbers or timestamps.
  • the compressor 100 and the decompressor 110 are required to maintain a common context.
  • the context 130 of the decompressor 110 is not consistent with the context 120 of the compressor 100 , header decompression will fail. This situation can occur when data packets are transmitted over unreliable, e.g. wireless, channels because packets may then be lost or damaged between compressor 100 and decompressor 110 .
  • update (UP) packets are provided for transmitting information contained in the context 120 of the compressor 100 , to the decompressor 110 .
  • UP packets the context 130 is updated.
  • NUP non-update
  • the packet stream to be compressed usually behaves very regularly. Most of the header fields are constant and do not change during the life-time of the stream. Some fields do change with each packet (e.g. sequence number and timestamp). If the values of these fields are synchronized to the sequence number and thus can be calculated from this number the stream is regular. Irregularities in these fields disturb this synchronization, e.g. because of a non-linear jump in the RTP-timestamp field. With an irregularity it is not possible to calculate the values of the changed fields from the sequence number. These irregularities might occur quite frequently, e.g. on the average every second for a conversational audio stream.
  • the length of NUP packets increases with time due to two reasons. If the stream shows irregularities the NUP packets that would be sent are larger, because these irregularities have to be included. If no irregularities in the stream occur, the length of the NUP packets also might increase with time, because of larger differences to the last update packets. To reduce the length of the NUP packets an update has to be performed, i.e. a number of UP packets are sent and if correctly received the context is updated.
  • One difficulty is to determine the number of UP packets to be sent for an update. If too many are sent, the context would already be updated and valid, while UP packets are still sent. This unnecessarily increases the transmitted bits and decreases the efficiency, because the UP packets are larger than NUP packets. On the other hand if not enough UP packets are sent the risk of losing the context is increased, because the probability increases that none of the sent UP packets is received.
  • burst errors are those errors by which several successive packets get lost.
  • three packets are assumed to get lost. Referring to FIG. 2 a, one UP packet and two NUP packets cannot be received by the decompressor. Since the decompressor now has an invalid context, the following NUP packets have to be discarded so that there is a total loss of nine packets at the receiver.
  • the number of consecutive UP packets has been increased to the amount of three. While sending a number of consecutive UP packets is usually more reliable because the probability that at least one of these UP packets is received correctly is quite high, the compression efficiency is decreased. Moreover, in the example of FIG. 2 b, the robustness has in fact not been improved, since due to the nature of the burst error, again nine packets cannot be decompressed at the receiver.
  • FIG. 2 c One approach to overcome the problems of burst errors is to use a sparse mode, as illustrated in FIG. 2 c.
  • a sparse mode means that in a fixed order, UP and NUP packets are sent, so that sending all UP packets in a row is avoided.
  • this sequence is UP-NUP-UP-NUP-NUP-UP-NUP-NUP-NUP-NUP-UP-NUP-NUP-NUP-NUP-NUP-NUP- . . .
  • FIG. 2 c even transmitting packets in the sparse mode might lead to a significant loss of data packets.
  • the present invention has been made in consideration of the above situation, and has as its primary object to provide a method and apparatus for transmitting data packets over an unreliable channel, capable of improving both the efficiency and robustness.
  • an object of the invention is to allow for dynamically controlling the update of the decompressor's context according to the channel quality.
  • a further object of the present invention is to reduce the mean header size even when channel quality varies.
  • a method of transmitting data packets over a channel where the data packets have compressed headers.
  • the method comprises the steps of compressing a header using a context; and transmitting a number of consecutive update packets, each containing data indicating said context.
  • the method further comprises the steps of determining the channel quality; and setting said number of update packets dependent on the determined channel quality.
  • the invention provides an apparatus for transmitting data packets over a channel, where the data packets have compressed headers.
  • the apparatus comprises a compressor for compressing a header using a context; transmission means for transmitting a number of consecutive update packets, each containing data indicating said context; means for determining the channel quality; and control means for setting said number of update packets dependent on the determined channel quality.
  • FIG. 1 illustrates a compressor/decompressor system, in which UP and NUP packets are used
  • FIGS. 2 a – 2 c illustrate time charts of UP-NUP sequences in case of a burst error
  • FIG. 3 illustrates the UP-NUP sequence during a context update phase according to the invention
  • FIGS. 4 a and 4 b illustrate compressor/decompressor systems in which the invention may preferably be used
  • FIG. 5 shows a general flow chart of the context update process according to the invention
  • FIGS. 6 a and 6 b are flow charts illustrating preferred embodiments of the process of setting the number of UP packets in each subsequence.
  • FIG. 7 is a flow chart illustrating the process of setting the total number of packets in the sequence according to a preferred embodiment of the invention.
  • the sequence of UP and NUP packets during the context update phase can be divided into a number of subsequences.
  • Each subsequence contains a number of UP packets followed by a number of NUP packets.
  • the following parameters are used for describing the UP-NUP sequence according to the invention.
  • the parameter p describes the total number of packets in the context update phase. This phase is entered whenever updating the context is considered necessary or at least useful, e.g. in case of context loss or, more generally, whenever an irregularity in the data stream has been detected.
  • the duration of the context update phase is chosen large enough to enable the decompressor to update its context.
  • the parameter k is the number of packets in each subsequence. In the preferred embodiment in FIG. 3 , this parameter is the same in each subsequence.
  • the parameter m i describes the number of UP packets in the i-th subsequence.
  • n i describes the number of NUP packets in the i-th subsequence.
  • FIGS. 4 a and 4 b illustrate compressor/decompressor systems in which the invention may preferably be applied.
  • the compressor receives measurement values concerning the channel quality from the measurement unit 400 .
  • the measurement unit 400 may be any entity, e.g. a physical layer entity, which can provide the compressor 100 with measurement values indicating the channel quality. Such values may include any kind of measures indicating, for example, noise properties in the channel or any bit or block errors. If actual measurements are not available, the measurement unit 400 might be a controller unit of the transmitter capable of performing any actions leading to at least estimated quality values.
  • the decompressor is capable of sending non-acknowledgement (NACK) messages to the compressor in case each of the UP packets of one subsequence are lost.
  • NACK non-acknowledgement
  • FIG. 5 illustrates the overall flow chart of updating the context 130
  • the process includes the steps 500 to 530 of setting each of the parameter m i , k, n i , and p.
  • the sequence of the steps illustrated in FIG. 5 may change. For instance, parameters p or k may be set first. Further, it is within the scope of the invention that the process of updating the context may include setting only some of the parameters while the remaining parameters are chosen to be constant or are set to default values.
  • step 500 the number m i of UP packets in each subsequence is set. As mentioned above, this number is preferably decreased by one from subsequence to subsequence. This scheme is chosen to take into account that the probability that at least one UP packet is correctly received, increases with the value of i. It is then in fact only necessary to find an optimum start value m 1 .
  • step 600 the compressor 100 obtains the current value of parameter m 1 . Then, in step 610 , a maximum and a minimum value for m 1 is read. The minimum and maximum values might for instance be set to two and six, respectively.
  • the compressor uses a start-up value instead.
  • the start-up value may preferably be set to the mean value of the minimum and maximum limits.
  • the compressor receives measurement values from measurement unit 400 which had been discussed above in the context of FIG. 4 a.
  • the values obtained in step 620 are preferably measurement values of the signal-to-noise ratio SNR or the block error rate BLER in the channel. If the SNR value is low, i.e. the BLER is high, a higher value of m 1 is required to increase the probability of correctly receiving the data packets at the decompressor.
  • step 630 It is then determined in step 630 , using the obtained measurement value, whether the channel condition has changed. If so, the parameter m 1 is updated in step 640 . Since the channel conditions might change very quickly and frequently, the value m 1 is adapted gradually, i.e. it is increased or decreased by a fixed amount depending on whether the channel quality has grown better or worse.
  • FIG. 6 b Another preferred embodiment of setting the number m 1 of UP packets in the first subsequence is shown in FIG. 6 b. This approach is preferably used when there are no measurement values available from measurement unit 400 .
  • the compressor determines in step 650 whether a NACK is received. If at least one UP packet of the first subsequence is received correctly, the decompressor 110 does not send a NACK message. Thus, if the compressor 100 does not receive a NACK within the complete procedure, the parameter m 1 is reduced by one for the next update procedure (step 660 ). If however a NACK is received, the parameter m 1 is increased in step 670 . This can preferably be done either by adding a predetermined value or by multiplying the current value by a predetermined factor.
  • this parameter i.e. the number of packets in each subsequence, will now be described in more detail (step 510 ).
  • this parameter is chosen to be constant for all blocks.
  • this constant value is set according to the codec properties.
  • some media codecs e.g. voice codecs
  • voice codecs e.g. voice codecs
  • the constant parameter k is set lower than this number x.
  • the compressor may for instance read the payload-type field of the RTP header to detect the used codec, if possible.
  • the compressor uses any available out-of-band signaling.
  • the parameter k is set accordingly.
  • the general properties of codecs might for this purpose be stored in, e.g., a look-up table of the compressor. If the compressor cannot determine suitable information, the parameter k is set to a value which is assumed not to harm the receiving application. In this case, a rather pessimistic approach is preferably used. Moreover, if no information on the codec used is available, the parameters m i can be slightly increased to nevertheless ensure robustness.
  • step 520 of the process depicted in FIG. 5 the numbers n i of NUP packets in each subsequence is set.
  • the process of updating the context comprises, with step 530 , a procedure of setting the total number p of packets in the sequence.
  • This procedure is depicted in more detail in FIG. 7 .
  • the parameter p is, in the preferred embodiment of the invention, set to a value large enough to give the decompressor sufficient time to react with a NACK message to any loss of data packets.
  • the parameter may advantageously be set according to the Round Trip Time RTT, preferably to a small multiple thereof. For this reason, the process of FIG. 7 involves an estimation of the current RTT value.
  • the process initiates a context loss in a silent period.
  • a silent period is a period of time where no packets are sent.
  • the compressor detects a silent period, e.g. whenever it cannot receive any RTP packet for a certain time.
  • step 700 it is determined in step 700 whether packets are sent. If there is a silent period detected, a wrong packet is sent in step 720 .
  • a wrong packet is a packet not having a correctly compressed header so that this packet will invalidate the context 130 of the decompressor 110 .
  • the decompressor will then immediately send back a NACK message which is received at the compressor 100 in step 730 .
  • the compressor estimates the RTT value in step 740 by calculating the time difference between the time of receiving the NACK and the time of sending the wrong packet. If it is determined in step 750 that the RTT value has changed, the parameter p is updated in step 760 .
  • the parameter p is chosen to be proportional to the RTT value.
  • the described process of setting the total number p of packets in the sequence is advantageous because this process is performed when an update procedure after a silent period is started anyway, because of some unpredictable gaps in the timestamp. Thus, there is no additional probability of losing the context 130 .
  • the described procedure of estimating the RTT value by sending a wrong packet is advantageous because the process can be performed whenever a silent period is detected.
  • the occurrence of a silent period is independent of any context loss and an adjustment of parameter p may thus be performed frequently even in channels of good quality.
  • the RTT estimation according to the invention is advantageous in that it allows a precise control of the parameter p. If the measurement would for instance be done using NACKs only, without initiating a context loss by sending a wrong packet, the measurement would result in the RTT value plus an additional time where at least one packet is lost and another packet is received. This additional time might be very high and is not computable.
  • the number of consecutive UP packets is set according to the channel quality.
  • the number of UP packets can be reduced.
  • the number of UP packets is increased so that there is still a robust connection between the transmitter and the receiver.
  • the mechanisms according to the invention are made not only adaptive to the current properties of the channel, but also to the type of packet stream. By making the sequence of UP and NUP packets dependent on both the channel quality and the packet stream properties, an even better compromise between compression efficiency and transmission robustness can be achieved.

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  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)
  • Mobile Radio Communication Systems (AREA)
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US20020027918A1 (en) * 2000-09-07 2002-03-07 Carsten Burmeister Method and apparatus for transmitting data packets
US20040034717A1 (en) * 2002-06-12 2004-02-19 Ghyslain Pelletier Method and apparatus for increased Internet Protocol (IP) headers compression performance by reporting cause of missing packets
US20070002850A1 (en) * 2005-06-29 2007-01-04 Guichard James N System and methods for compressing message headers
US20070104218A1 (en) * 2005-11-08 2007-05-10 Microsoft Corporation Adapting a communication network to varying conditions
WO2007064455A1 (en) * 2005-11-30 2007-06-07 Microsoft Corporation Predicting degradation of a communication channel below a threshold based on data transmission errors
US7330902B1 (en) * 1999-05-10 2008-02-12 Nokia Corporation Header compression
US20090052452A1 (en) * 2007-08-23 2009-02-26 Keyur Patel Signaling compression information using routing protocols
US20090249172A1 (en) * 2008-03-26 2009-10-01 Qualcomm Incorporated Methods and apparatus for improved decoding of bursts that include multiple concatenated protocol data units
US20090257372A1 (en) * 2008-04-09 2009-10-15 Qualcomm Incorporated Methods and apparatus for improved decoding of hybrid automatic repeat request transmissions
US8705537B1 (en) * 2012-06-10 2014-04-22 Andrei Teodor Borac Eventually-consistent data stream consolidation

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JP3643360B2 (ja) * 2002-08-12 2005-04-27 松下電器産業株式会社 受信装置及び通信方法
EP1432196A1 (en) * 2002-12-20 2004-06-23 Matsushita Electric Industrial Co., Ltd. Control traffic compression method in media data transmission
DE10320157B3 (de) * 2003-05-06 2004-11-11 Infineon Technologies Ag Kanalqualifizierung und -selektion in einem mehrkanaligen Funksystem durch Paketfehlerraten-Messung
DE10320176B3 (de) * 2003-05-06 2004-12-09 Infineon Technologies Ag Verfahren zur Selektion der Frequenzkanäle eines ein Frequenzsprungverfahren verwendenden Funksystems
WO2007050593A2 (en) * 2005-10-25 2007-05-03 William Marsh Rice University Method and apparatus for signal detection, classification, and estimation from compressive measurements
CN1992671B (zh) * 2005-12-28 2010-08-11 上海原动力通信科技有限公司 第三代演进系统中传输ip头压缩数据包的方法
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US20140149611A1 (en) * 2012-11-26 2014-05-29 Qualcomm Incorporated CHANNEL CONDITION AWARE USB DATA DELIVERY OVER Wi-Fi WITH DIFFERENTIAL TREATMENT ON DISTINCT USB ENDPOINTS
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CN108400837B (zh) * 2017-02-06 2022-08-02 中兴通讯股份有限公司 数据发送方法及终端设备
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US7330902B1 (en) * 1999-05-10 2008-02-12 Nokia Corporation Header compression
US7158518B2 (en) * 2000-09-07 2007-01-02 Matsushita Electric Industrial Co., Ltd. Method and apparatus for transmitting data packets
US20020027918A1 (en) * 2000-09-07 2002-03-07 Carsten Burmeister Method and apparatus for transmitting data packets
US20040034717A1 (en) * 2002-06-12 2004-02-19 Ghyslain Pelletier Method and apparatus for increased Internet Protocol (IP) headers compression performance by reporting cause of missing packets
US8619592B2 (en) * 2002-06-12 2013-12-31 Telefonaktiebolaget L M Ericsson (Publ) Method and apparatus for increased internet protocol (IP) headers compression performance by reporting cause of missing packets
US20070002850A1 (en) * 2005-06-29 2007-01-04 Guichard James N System and methods for compressing message headers
US7602778B2 (en) * 2005-06-29 2009-10-13 Cisco Technology, Inc. System and methods for compressing message headers
US20070104218A1 (en) * 2005-11-08 2007-05-10 Microsoft Corporation Adapting a communication network to varying conditions
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US8396041B2 (en) 2005-11-08 2013-03-12 Microsoft Corporation Adapting a communication network to varying conditions
WO2007064455A1 (en) * 2005-11-30 2007-06-07 Microsoft Corporation Predicting degradation of a communication channel below a threshold based on data transmission errors
US9106433B2 (en) 2005-11-30 2015-08-11 Microsoft Technology Licensing, Llc Predicting degradation of a communication channel below a threshold based on data transmission errors
US8381047B2 (en) 2005-11-30 2013-02-19 Microsoft Corporation Predicting degradation of a communication channel below a threshold based on data transmission errors
US20090052452A1 (en) * 2007-08-23 2009-02-26 Keyur Patel Signaling compression information using routing protocols
US7885294B2 (en) * 2007-08-23 2011-02-08 Cisco Technology, Inc. Signaling compression information using routing protocols
US20090249172A1 (en) * 2008-03-26 2009-10-01 Qualcomm Incorporated Methods and apparatus for improved decoding of bursts that include multiple concatenated protocol data units
US8126014B2 (en) 2008-04-09 2012-02-28 Qualcomm Incorporated Methods and apparatus for improved decoding of hybrid automatic repeat request transmissions
US20090257372A1 (en) * 2008-04-09 2009-10-15 Qualcomm Incorporated Methods and apparatus for improved decoding of hybrid automatic repeat request transmissions
US8705537B1 (en) * 2012-06-10 2014-04-22 Andrei Teodor Borac Eventually-consistent data stream consolidation

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DE60020117T2 (de) 2005-10-06
EP1187417B1 (en) 2005-05-11
CA2353263A1 (en) 2002-03-07
DE60020117D1 (de) 2005-06-16
JP2002124989A (ja) 2002-04-26
CN1343056A (zh) 2002-04-03
JP3535852B2 (ja) 2004-06-07
US20020027882A1 (en) 2002-03-07
EP1187417A1 (en) 2002-03-13
CN1156123C (zh) 2004-06-30
CA2353263C (en) 2007-01-23

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